What is OTEC?

OTEC extracts energy from the temperature differential of the warm surface water and
the cold water in the deep ocean. The process consists of pumping cold ocean
water to the surface and using the temperature differential between this and
warm surface water to run a thermal engine and generate electricity.

It is ideally suited to warm tropical waters such as those found in the Philippines and countries along
the equatorial belt, particularly those with deep ocean close to land and with
legacy polar currents at depth. The ideal surface water temperature is 28
degrees Celsius while the ideal cold water temperature is 5 deg Celsius at 1000 m deep.

To produce electricity a differential minimum of 20 degrees Celsius is necessary.
The higher the difference the more power it can generate.

Due to the relatively low temperature differentials, OTEC requires high engineering skills.
Although the technology has been proven in small pilot plants the upfront
development costs remain high but large pre-commercial production as the next
level of development may be feasible with government support measures such as Feed-in Tariff.

OTEC’s major advantage when compared to other renewable energies is its potential to produce
electricity reliably and at a constant rate all year round. Additionally as a
primarily offshore installation it has minimal onshore impact.

How does it work? There are three (3) basic designs to generate electricity:

Open Cycle OTEC as represented in the diagram above produces drinking water as by-product.
Warm sea water is introduced into an evaporation chamber to remove the
salt in the water and generate steam like the hot air you get when a
kettle boils. The hot air then powers a turbine and create electricity.
After it powers the turbine it is then collected into a condensing chamber
which is cooled by the water from the deep ocean. This turns the hot air
back into liquid producing desalinated water which can be used as drinking
water.

In Closed Cycle OTEC warm surface water is used to
heat a working fluid such as ammonia. It boils at low temperature without the need for firing and
create vapours to drive a turbine. Using the cold water from deep ocean
the working fluid is then cooled back to its liquid state so that the warm
surface water can heat it again to repeat the process. No desalinated
water is produced as by-product.

One can combine both features in Closed and Open Cycle using
Hybrid Cycle OTEC.

In a hybrid cycle the warm surface water is introduced into an
evaporation chamber to generate steam – just like the Open Cycle. The
steam produced is then used to heat and vapourise the working fluid to drive the
turbine and produce electricity. Just like the Closed Cycle the working
fluid is
then cooled by deep ocean water back to its liquid state. It is then
possible to condense the steam from the warm surface water to produce
drinking water.